This invention relates to a fuel cell and particularly to an improved fuel cell suitable for the application to a Molten Carbonate Fuel Cell or Phosphoric Acid Fuel Cell.
Generally, a plurality of unit cells are laid upon one another to form a fuel cell. A single unit cell is produced by holding an electrolytic plate (matrix) in which an electrolyte is impregnated, between a pair of electrodes (anode and cathode) and further holding them between a pair of separators. In order to produce a greater electric power by the fuel cell, it is necessary to increase the effective areas of the electrodes of the unit cell and stack a great number of unit cells. A fuel cell integrally formed by such electrodes, electrolytic plate and separators is proposed as disclosed, for example, in Japanese Patent Un-Examined Publication Nos. 58-216365, 58-220368, 59-27467 and 59-27468.
If the electrodes, electrolytic plate and separators are simply increased in size for increasing the capacity of the unit cell, the following problems occur.
One of the problems is that it is technically difficult to produce thin electrodes and electrolytic plate with large area, and smooth surfaces. Thus their sizes are limited. Particularly when the unit cells are stacked in terms of space effect, it is desired to use thinner electrodes and electrolytic plate. Secondly, larger area electrodes and electrolytic plate have less mechanical strength. That is, since the fuel cell is operated in a relatively high-temperature atmosphere, it is stressed by the temperature-change cycle with the result that cracks or crevices occur in the electrodes and electrolytic plate. Therefore, the reaction gas and electrolyte leak via the cracks or crevices, shortening the life of the cell. Particularly in the case of a Molten Carbonate Fuel Cell, the operating temperature reaches 650.degree. C. at which a thin electrolytic plate made of ceramics suffers a great stress detrimental to its strength. Thirdly, it becomes difficult for the electrolyte to be supplied to the large-sized fuel cell. When the fuel cell is operated for a long period of time, the electrolyte is gradually consumed so that the cell performance is reduced. Thus, in order to restore the cell performance to the initial state, it is necessary to supply the electrolyte properly. Also, it is difficult to uniformly impregnate the electrolyte into all parts of the electrolytic plate of large size and it takes a long time to do so.
These problems limited to make the unit cell in smaller size.